In discussing his work of preaching the gospel, the apostle Paul told the Corinthians, "But we have this treasure in earthen vessels, that the excellence of the power may be of God and not of us" (2 Cor. 4:7).
It was a practice among some of the ancients to carry great treasures of gold and silver in vessels of clay. Brother Melvin Curry made the following observation regarding this practice: "...valuable treasures captured in military battles were displayed as the spoils of war. In such parades gold and silver coins were sometimes carried in earthen vessels, which are made of clay... Paul does not choose the figure of expensive vessels that are made of gold, silver, ivory, or glass (as he alluded to in 2 Timothy 2:20); rather, he uses that of containers created from ordinary clay. Such clay jars are usually of little significance when compared to the treasures they contain" (Truth Commentaries, the Book of 2 Corinthians, page 158).
The "earthen vessel" in this figure is the physical body of the preacher. The "treasure" is the gospel. The gospel is the important thing, not the preacher. It is the gospel that saves man (Rom. 1:16), not the talent or ability of the preacher. Preachers come and go (earthen vessels wear out and are replaced), but the gospel is God's eternal message of salvation.
God has chosen to save man through the gospel (1 Cor. 1:21). God could have arranged for the gospel to be preached to man through angels, through a direct outpouring of the Holy Spirit, through visions or dreams, through messages spelled out in the stars of heaven, etc. However, in His wisdom, God has seen fit for the gospel to be passed along through men. Specifically, those who are saved by the gospel are the ones who are to carry the gospel to the lost.
Consider the pattern set forth in the book of Acts.
In Acts chapter two, the Holy Spirit is poured out on the apostles (Acts 2:1-4). The signs accompanying this outpouring (sound of a mighty rushing wind and speaking in tongues) gather a crowd who begin to ask questions about what they are hearing. The Holy Spirit was very much involved in this event, but it was Peter (a man) who preached the gospel to the Jews.
In Acts chapter eight, an angel told Philip to leave Samaria and travel towards a certain road. When he reached his destination, the Holy Spirit told him to go near an approaching chariot. When he did, he heard a man from Ethiopia reading the prophet Isaiah. Soon Philip was preaching to the man and baptized him (Acts 8:26-40). Both an angel and the Holy Spirit were involved in this account of conversion, but it was Philip (a man) who preached the gospel to the Ethiopian.
In Acts chapter nine, the Lord appeared to Saul while he was on the road to Damascus. The Lord told Saul to go into the city where he would be told what he must do (Acts 9:1-6). Ananias came to Saul and told him to arise and be baptized, and wash away his sins, calling on the name of the Lord (Acts 22:16). The Lord spoke to Saul, but it was Ananias (a man) who preached the gospel to Saul.
In Acts chapter ten, an angel appeared to Cornelius and told him to send for Peter who would tell him what he must do (Acts 10:1-6). Cornelius was in Caesarea. Peter was in Joppa, about 32 miles away. Why didn't the angel tell Cornelius what he had to do to be saved? It sure would have saved some time. It was Peter (a man) who preached the gospel to Cornelius and his household.
Have you noticed a pattern? Angels, the Holy Spirit, and even the Lord Himself, were involved in these accounts of conversion in the book of Acts, but in every incident, it was a man who told lost sinners what they had to do to be saved.
The same thing is true today. Indeed, a great treasure has been entrusted to us as earthen vessels. It is our place and our responsibility to tell people what they have to do to be saved. We are to help the lost find and hear the gospel.